The suggestions to check the connector are great. I had the same problem with my truck/trailer on a recent trip. I cleaned the connectors. Everything worked on the trailer as you mentioned. The disconnected message eventually came on and didn't reset. I stopped at a rest stop and checked under my trailer. Although not visible, one brake wire was cut where it was zip-tied to the axle. The wire insulation appeared as one piece, so the cut was not obvious while laying on the ground. Anyway, test-pulling on the wire pulled it apart. I spliced it back and taped it. No more messages the entire trip, even over rough roads. I made permanent repairs when we got back home....no disconnect messages to date. Before I made repairs, I guess the cut ends of the wire could re-touch and the problem would go away until I hit rough roads.